<div class="container"></div>

<style>
/* From Uiverse.io by elijahgummer  - Tags: simple, blue, modern, pattern */
.container {
  width: 100%;
  height: 100%;
  position: relative;
  background: #f0f0f0;
}

.container::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: linear-gradient(
      45deg,
      #3498db 25%,
      transparent 25%,
      transparent 50%,
      #3498db 50%,
      #3498db 75%,
      transparent 75%,
      transparent
    ),
    linear-gradient(
      -45deg,
      #3498db 25%,
      transparent 25%,
      transparent 50%,
      #3498db 50%,
      #3498db 75%,
      transparent 75%,
      transparent
    );
  background-size: 20px 20px;
  opacity: 0.8;
}

</style>
    